WO2021132203A1 - Separator for nonaqueous electrolyte secondary batteries, nonaqueous electrolyte secondary battery, and method for producing separator for nonaqueous electrolyte secondary batteries - Google Patents

Abstract

This separator for nonaqueous electrolyte secondary batteries contains a polymer compound and a solid electrolyte, and has a pore volume of 0.06 cm3/g or less.

Description

Method for manufacturing separator for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and separator for non-aqueous electrolyte secondary battery

The present disclosure relates to a method for manufacturing a separator for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a separator for a non-aqueous electrolyte secondary battery.

The separator for non-aqueous electrolyte secondary batteries may contain an inorganic filler for the purpose of improving heat resistance and ion permeability. Patent Document 1 discloses a separator having excellent shape stability without shrinking even at a high temperature by containing an inorganic filler and a water-soluble polymer having a predetermined structure.

International Publication No. 2018/079474

The characteristics of the separator for non-aqueous electrolyte secondary batteries change depending on the pore size, and the characteristics often have a trade-off relationship. A separator having a large pore size of several hundred nm has a feature that the penetration rate of the electrolytic solution is high, but dendrites easily grow through the pores, so that an internal short circuit is likely to occur. On the other hand, a separator having a small pore size can suppress an internal short circuit, but the permeation rate of the electrolytic solution is slow.

The separator for a non-aqueous electrolyte secondary battery, which is one aspect of the present disclosure, contains a polymer compound and a solid electrolyte, and has a pore volume of 0.06 cm ³ / g or less.

The non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes the above-mentioned separator for a non-aqueous electrolyte secondary battery, a positive electrode, a negative electrode, and a non-aqueous electrolyte.

One aspect of the present disclosure is a method for producing a separator for a non-aqueous electrolyte secondary battery, which comprises a slurry preparation step of mixing a solution prepared by dissolving a polymer compound in an ionic liquid and a solid electrolyte to prepare a slurry. A gelling step in which the slurry is applied to the surface of the substrate to prepare a coating film, and the coating film is gelled by substituting with an organic poor solvent having a lower solubility of the polymer compound than the ionic liquid. , A drying step of drying the gelled film to obtain a composite film.

According to the separator for a non-aqueous electrolyte secondary battery, which is one aspect of the present disclosure, it is possible to improve the permeation rate of the electrolytic solution while suppressing an internal short circuit.

It is a vertical sectional view of the non-aqueous electrolyte secondary battery which is an example of embodiment.

Hereinafter, an example of an embodiment of the non-aqueous electrolyte secondary battery separator according to the present disclosure and the non-aqueous electrolyte secondary battery using the non-aqueous electrolyte secondary battery separator will be described in detail. In the following, a cylindrical battery in which a wound electrode body is housed in a bottomed cylindrical outer can is illustrated, but the outer body is not limited to the cylindrical outer can, for example, a square outer can. It may be an exterior body composed of a laminated sheet including a metal layer and a resin layer. Further, the electrode body may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated via a separator.

FIG. 1 is a vertical cross-sectional view of a cylindrical secondary battery 10 which is an example of an embodiment. In the secondary battery 10 shown in FIG. 1, an electrode body 14 and a non-aqueous electrolyte (not shown) are housed in an exterior body 15. The electrode body 14 has a winding structure in which the positive electrode 11 and the negative electrode 12 are wound via the separator 13. In the following, for convenience of explanation, the sealing body 16 side will be referred to as “top” and the bottom side of the exterior body 15 will be referred to as “bottom”.

The inside of the secondary battery 10 is sealed by closing the opening end of the exterior body 15 with the sealing body 16. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode lead 19 extends upward through the through hole of the insulating plate 17 and is welded to the lower surface of the filter 22 which is the bottom plate of the sealing body 16. In the secondary battery 10, the cap 26, which is the top plate of the sealing body 16 electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends to the bottom side of the exterior body 15 through the through hole of the insulating plate 18 and is welded to the inner surface of the bottom portion of the exterior body 15. In the secondary battery 10, the exterior body 15 serves as a negative electrode terminal. When the negative electrode lead 20 is installed at the terminal portion, the negative electrode lead 20 passes through the outside of the insulating plate 18 and extends to the bottom side of the exterior body 15 and is welded to the inner surface of the bottom portion of the exterior body 15.

The exterior body 15 is, for example, a bottomed cylindrical metal exterior can. A gasket 27 is provided between the exterior body 15 and the sealing body 16 to ensure the internal airtightness of the secondary battery 10. The exterior body 15 has a grooved portion 21 that supports the sealing body 16 and is formed by pressing, for example, a side surface portion from the outside. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior body 15, and the sealing body 16 is supported on the upper surface thereof via the gasket 27.

The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are laminated in order from the electrode body 14 side. Each member constituting the sealing body 16 has, for example, a disk shape or a ring shape, and each member except the insulating member 24 is electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their central portions, and an insulating member 24 is interposed between the peripheral portions thereof. When the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 breaks, which causes the upper valve body 25 to swell toward the cap 26 side and separate from the lower valve body 23, thereby cutting off the electrical connection between the two. .. When the internal pressure further rises, the upper valve body 25 breaks and gas is discharged from the opening 26a of the cap 26.

Hereinafter, the positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte constituting the electrode body 14 will be described in detail, particularly the separator 13.

[Positive electrode]
The positive electrode 11 has a positive electrode core body and a positive electrode mixture layer provided on the surface of the positive electrode core body. As the positive electrode core body, a metal foil stable in the potential range of the positive electrode 11 such as aluminum, a film in which the metal is arranged on the surface layer, or the like can be used. The thickness of the positive electrode core is, for example, 10 μm to 30 μm. The positive electrode mixture layer contains a positive electrode active material, a binder, and a conductive material, and is preferably provided on both sides of the positive electrode core body excluding the portion to which the positive electrode lead 19 is connected. For the positive electrode 11, for example, a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive material, and the like is applied to the surface of a positive electrode core, the coating film is dried, and then compressed to form a positive electrode mixture layer. It can be manufactured by forming it on both sides of the core body.

Examples of the positive electrode active material contained in the positive electrode mixture layer include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Lithium transition metal oxides, for example, _{Li x CoO 2, Li x NiO} 2, Li x MnO 2, Li x Co y Ni 1-y O 2, Li x Co y M 1-y O z, Li x Ni 1- _{y M y O z, Li x} Mn 2 O 4, Li x Mn 2-y M y O 4, LiMPO 4, Li 2 MPO 4 F (M; Na, Mg, Sc, Y, Mn, Fe, Co, Ni , Cu, Zn, Al, Cr, Pb, Sb, B, 0 <x ≦ 1.2, 0 <y ≦ 0.9, 2.0 ≦ z ≦ 2.3). These may be used alone or in admixture of a plurality of types. In that it can increase the capacity of the nonaqueous electrolyte secondary battery, the positive electrode active _{material, Li x NiO 2, Li x} Co y Ni 1-y O 2, Li x Ni 1-y M y O z ( M; At least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0 <x≤1.2, 0 <y≤0. It is preferable to contain a lithium nickel composite oxide such as 9.9, 2.0 ≦ z ≦ 2.3).

Examples of the conductive material contained in the positive electrode mixture layer include carbon materials such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes, carbon nanofibers, and graphite. These may be used alone or in combination of two or more.

Examples of the binder contained in the positive electrode mixture layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. .. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or salts thereof, polyethylene oxide (PEO) and the like. These may be used alone or in combination of two or more.

[Negative electrode]
The negative electrode 12 has a negative electrode core body and a negative electrode mixture layer provided on the surface of the negative electrode core body. As the negative electrode core, a metal foil stable in the potential range of the negative electrode 12 such as copper, a film in which the metal is arranged on the surface layer, or the like can be used. The thickness of the negative electrode core is, for example, 5 μm to 15 μm. The negative electrode mixture layer contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode core body excluding the portion to which the negative electrode lead 20 is connected, for example. For the negative electrode 12, for example, a negative electrode mixture slurry containing a negative electrode active material and a binder is applied to the surface of the negative electrode core body, the coating film is dried, and then compressed to form the negative electrode mixture layer on both sides of the negative electrode core body. It can be produced by forming in. Further, a conductive material may be added to the negative electrode mixture slurry. The conductive material can make the conductive path uniform.

As the binder contained in the negative electrode mixture layer, a fluororesin such as PTFE or PVdF, PAN, polyimide, acrylic resin, polyolefin or the like may be used as in the case of the positive electrode 11, but styrene-is preferable. Polyolefin rubber (SBR) is used. Further, these resins may be used in combination with CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA) and the like. Examples of the conductive material contained in the negative electrode mixture layer include carbon black, acetylene black, ketjen black, carbon nanotubes, and carbon nanofibers.

[Separator]
The separator 13 contains a polymer compound and a solid electrolyte. In other words, the separator 13 contains a polymer compound as a matrix and a solid electrolyte as an inorganic filler. Pore volume of the separator 13 is less 0.06 cm ³ / g, preferably not more than 0.05 cm ³ / g. As a result, an internal short circuit can be suppressed while ensuring ionic conductivity between the positive electrode and the negative electrode. Here, the pore volume can be measured using nitrogen gas by, for example, a commercially available measuring device such as BELSORP-miniX manufactured by Microtrac Bell.

The thickness of the separator 13 is preferably 0.2 μm or more and 10 μm or less, and more preferably 0.4 μm or more and 1 μm or less. If the thickness of the separator 13 is less than 0.2 μm, the strength is insufficient. If the thickness of the separator 13 exceeds 10 μm, the volume of the separator that does not contribute to charging / discharging increases in the internal space of the battery, and the density of the battery decreases.

The mass ratio of the polymer compound to the solid electrolyte in the separator 13 is preferably 100: 1 to 100: 100,000, more preferably 100: 1 to 100: 10000, and particularly preferably 100: 1 to 100: 400. The separator 13 may contain additives other than the polymer compound and the solid electrolyte as long as the object of the present disclosure is not impaired.

Examples of the polymer compound contained in the separator 13 include olefin resins such as polyethylene and polypropylene, cellulose, and cellulose derivatives. Cellulose is preferable as the polymer compound. Cellulose is inexpensive and dissolves in an ionic liquid, so that the separator 13 can be easily thinned by a production method described later.

The solid electrolyte contained in the separator 13 includes Li ₇ La ₃ Zr ₂ O _{12 (LLZ) having a garnet type structure, Li 1 + x} Al _x Ti _2-x P ₃ O ₁₂ (LATP) having a NASICON type structure, and a perovskite type. _{Examples thereof include La 2 / 3-x} Li _x TiO ₃ (LLT) having a structure, and lithium ion-containing polyethylene oxide (Li ⁺ · PEO). Here, LLZ, LATP, and LLT include those in which some of the elements contained in the above general formula are replaced with other additive elements.

As the solid electrolyte, LATP is preferable from the viewpoint of ionic conductivity. As the LATP, for example, ^{a LICGC TM} manufactured by O'Hara, which is represented by _{Li 1 + x + y} Al _x Ti _2-x Si _y P _3-y O ₁₂ , can be used.

The solid electrolyte may be powder. The average particle size is, for example, 0.1 μm or more and 10 μm or less, preferably 0.4 μm or more and 1 μm or less. Here, the average particle size means a particle size in which the cumulative frequency is 50% from the smaller particle size in the volume-based particle size distribution, and is also called a median size. The particle size distribution of the solid electrolyte can be measured using water as a dispersion medium using a laser diffraction type particle size distribution measuring device (for example, MT3000II manufactured by Microtrac Bell Co., Ltd.).

Lithium ions may be allowed to move inside the separator 13 by contacting and connecting a plurality of solid electrolytes from one surface to the other surface of the separator 13, and the thickness of the separator 13 is the average particle size of the solid electrolyte. By doing the following, one solid electrolyte particle may penetrate the separator. From the viewpoint of the ease of movement of lithium ions, it is preferable that the thickness of the separator is equal to or smaller than the average particle size of the solid electrolyte.

A heat-resistant layer containing a heat-resistant material may be formed on the surface of the separator 13. Examples of the heat-resistant material include polyamide resins such as aliphatic polyamides and aromatic polyamides (aramid), and polyimide resins such as polyamideimide and polyimide.

Hereinafter, an example of a method for manufacturing the separator 13 will be described.

First, in the slurry preparation step, a slurry is prepared by mixing a solution prepared by dissolving a polymer compound in an ionic liquid and a solid electrolyte. An ionic liquid is a salt containing anions and cations and is a liquid at room temperature. As the ionic liquid for dissolving cellulose, a commercially available ionic liquid for dissolving cellulose can be used. As the ionic liquid, an alkylimidazolium salt or the like can be used, and examples of the salt type include chloride, acetate, phosphate and the like.

The mass ratio of the ionic liquid to the polymer compound in the slurry is, for example, 100: 0.2 to 100: 15. Within this range, the polymer compound dissolves in the ionic liquid, and the separator 13 can be produced by film formation. The solid electrolyte can be added, for example, from 1 part by mass to 100,000 parts by mass with respect to 100 parts by mass of the polymer compound.

Next, in the gelling step, the slurry is applied to the surface of the substrate to prepare a coating film, and the coating film is gelled by substituting with an organic poor solvent having a lower solubility of the polymer compound than the ionic liquid. Make a membrane. As the substrate on which the slurry is applied, for example, a flat resin, glass, or metal substrate can be used. Ethyl acetate can be exemplified as an organic antisolvent to be replaced with an ionic liquid. The substrate on which the coating film is formed on the surface may be immersed in acetone and then immersed in ethyl acetate to relay the acetone and replace the ionic liquid with ethyl acetate.

In the drying step, the gelled film is dried to obtain a composite film. The gelled membrane shrinks due to drying, but according to the above-mentioned production method, the shrinkage of the polymer compound in the gelled membrane is suppressed, so that voids are formed between the polymer compound and the solid electrolyte. Can be suppressed. The obtained composite film may be used as it is as the separator 13, or the composite film may be further subjected to a post-process.

[Non-aqueous electrolyte]
The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to the liquid electrolyte (electrolyte solution), and may be a solid electrolyte using a gel polymer or the like. As the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of these can be used. The non-aqueous solvent may contain a halogen substituent in which at least a part of hydrogen in these solvents is substituted with a halogen atom such as fluorine.

Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and methylpropyl carbonate. , Ethylpropyl carbonate, chain carbonate such as methyl isopropyl carbonate, cyclic carboxylic acid ester such as γ-butyrolactone, γ-valerolactone, methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate, Examples thereof include chain carboxylic acid esters such as γ-butyrolactone.

Examples of the above ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahexyl, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4. -Cyclic ethers such as dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether , Dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxy toluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxy Chain ethers such as ethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl, etc. Kind and so on.

As the halogen substituent, it is preferable to use a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC), a fluorinated chain carbonate, a fluorinated chain carboxylic acid ester such as methyl fluoropropionate (FMP), or the like. ..

The electrolyte salt is preferably a lithium salt. _Examples of the lithium _{salt, LiBF 4, LiClO 4, LiPF} 6, LiAsF 6, LiSbF 6, LiAlCl 4, LiSCN, LiCF 3 SO 3, LiCF 3 CO 2, Li (P (C 2 O 4) F 4), LiPF _6-x (C _n F _{2n + 1} ) _x (1 <x <6, n is 1 or 2), LiB ₁₀ Cl ₁₀ , LiCl, LiBr, LiI, lithium _{chloroborane, lithium lower aliphatic carboxylate, Li 2} B ₄ O ₇ , borates such as Li (B (C ₂ O ₄ ) F ₂ ), LiN (SO ₂ CF ₃ ) ₂ , LiN (C ₁ F _{2l + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) {l , M is an integer of 1 or more} and other imide salts. As the lithium salt, these may be used individually by 1 type, or a plurality of types may be mixed and used. _{Of these, LiPF 6} is preferably used from the viewpoint of ionic conductivity, electrochemical stability, and the like. The concentration of the lithium salt is preferably 0.8 to 1.8 mol per 1 L of the solvent.

Hereinafter, the present disclosure will be further described with reference to Examples, but the present disclosure is not limited to these Examples.

<Example>
[Making a separator]
Cellulose having a mass average molecular weight of about 300,000 was dissolved in 1-ethyl-3-methylimidazolium diethyl phosphate, which is an ionic liquid for dissolving cellulose. To 1 part by mass of cellulose, 2 parts by mass of LICGC powder (manufactured by O'Hara, particle size 1 μm) was added and mixed uniformly to prepare a slurry. A separator was prepared by forming a film on a glass plate by a casting method, removing the ionic liquid with acetone, substituting acetone with ethyl acetate, and then air-drying the glass plate. With respect to the prepared separator, the adsorption isotherm due to nitrogen adsorption was measured using BELSORP-miniX manufactured by Microtrac Bell, and the pore volume was determined by the BJH method. As a result, ^{it was 0.047 cm 3} / g. The thickness of the separator was 60 μm.

[Preparation of positive electrode]
_{LiNi 0.5} Co _0.2 Mn _0.3 O2 was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) are mixed at a solid content mass ratio of 100: 3: 1, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added and then kneaded. To prepare a positive electrode mixture slurry. The positive electrode mixture slurry is applied to both sides of the positive electrode core made of aluminum foil, the coating film is dried, and then the coating film is rolled using a roller and cut to a predetermined electrode size to form the positive electrode core. A positive electrode having a positive electrode mixture layer formed on both sides was obtained. An exposed portion where the surface of the positive electrode core was exposed was provided on a part of the positive electrode.

[Preparation of negative electrode]
Li metal was pressed against the Ni mesh as the negative electrode active material to fix it, and the negative electrode was cut to a predetermined electrode size to obtain a negative electrode. An exposed portion where the surface of the negative electrode core was exposed was provided on a part of the negative electrode.

[Preparation of electrolyte]
_{Lithium hexafluorophosphate (LiPF 6} ) was added to a mixed solvent in which fluoroethylene carbonate (FEC) and methyl 3,3,3-trifluoropropionate (FMP) were mixed in a volume ratio of 2: 8. An electrolytic solution (non-aqueous electrolyte) dissolved at a concentration of 0.0 mol / liter was prepared.

[Preparation of test cell]
An electrode body was produced by attaching an aluminum lead to the exposed portion of the positive electrode and a nickel lead to the exposed portion of the negative electrode, and arranging the positive electrode and the negative electrode facing each other via the prepared separator. This electrode body was housed in an exterior body made of an aluminum laminated sheet, and after injecting the non-aqueous electrolyte, the opening of the exterior body was sealed to obtain a test cell.

[Evaluation of permeation rate of electrolyte]
The separator produced above was sandwiched between hypersheet gaskets and fixed to the center of the H-shaped cell. LiTFSI / DME (molar ratio LiTFSI: DME = 1:10) is placed in the left chamber of the H-type cell, and LiTFSI / FEC + FMP (molar ratio LITFSI: FMP = 1:10) is placed in the right chamber. The liquid was collected and the concentration of DME was quantitatively analyzed by GC-MS. The higher the DME concentration of the liquid in the right ventricle, the faster the permeation rate of the electrolytic solution.

[Evaluation of short circuit suppression]
The test cell produced above was charged with a constant current (CC) of 0.01 C until the battery voltage reached 4.7 V in a temperature environment of 25 ° C., and it was confirmed whether or not there was a voltage drop during charging. Those without a voltage drop during charging were evaluated as "○" as those without an internal short circuit, and those with a voltage drop were evaluated as "x" as having an internal short circuit.

<Comparison example>
Evaluation was carried out in the same manner as in Example 1 except that the slurry described in Example 1 was formed on a glass plate by a casting method, the ionic liquid was removed with ultrapure water, and the slurry was naturally dried to prepare a separator. It was.

Table 1 shows the evaluation results of Examples and Comparative Examples. Table 1 shows the thickness of the separator and the pore volume together with the evaluation results.

As shown in Table 1, it was found that the separator of the example had an effect of suppressing a short circuit as compared with the separator of the comparative example. In addition, the separator of the example had a faster permeation rate of the electrolytic solution than the separator of the comparative example. This is because the use of ethyl acetate as the solvent increased the nano-sized pores in the separator, while the smaller pore volume was due to the increase in the nano-sized pores between the solid electrolyte and the matrix. It is presumed that this is because the effect of the reduction of the voids is large.

10 Rechargeable battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Electrode body 15 Exterior body 16 Sealing body 17, 18 Insulating plate 19 Positive electrode lead 20 Negative electrode lead 21 Grooving part 22 Filter 23 Lower valve body 24 Insulating member 25 Upper valve body 26 Cap 26a Open Part 27 Gasket

Claims (6)

1. Contains polymer compounds and solid electrolytes
   A separator for a non-aqueous electrolyte secondary battery having a pore volume of 0.06 cm ^{3 / g or less.}
2. The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness is 0.2 μm or more and 10 μm or less.
3. The separator for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the polymer compound is cellulose.
4. The separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the solid electrolyte is LATP.
5. A non-aqueous electrolyte secondary battery comprising the separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, a positive electrode, a negative electrode, and a non-aqueous electrolyte.
6. A slurry preparation step of mixing a solution obtained by dissolving a polymer compound in an ionic liquid and a solid electrolyte to prepare a slurry.
   The slurry is applied to the surface of a substrate to prepare a coating film, and the coating film is gelled by substituting with an organic poor solvent having a lower solubility of the polymer compound than the ionic liquid to prepare a gelled film. Gelling process and
   A method for producing a separator for a non-aqueous electrolyte secondary battery, which comprises a drying step of drying the gelled film to obtain a composite film.

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